Method and System for Monitoring a Sensor Arrangement

ABSTRACT

The invention relates to a method and a system for monitoring a sensor arrangement comprising a vibrating gyroscope. Said vibrating gyroscope is used as a resonator and is part of at least one control circuit that excites the vibration gyroscope by feeding an excitation signal with its natural frequency. An output signal can be tapped from the vibrating gyroscope from which the excitation signal can be derived by filtering and amplification. The invention is characterized in that a first value of temperature change is calculated from the difference of the actual value of the natural frequency and a value of the natural frequency measured at a reference temperature during a comparison and stored in a memory, and the temperature coefficient of the natural frequency in relation to the measured temperature. A second value of the temperature change is calculated from the difference between the output values of a temperature sensor at the actual temperature and at a reference temperature stored in the memory and the temperature coefficient of the temperature sensor. The two calculated values are compared and an error signal is produced in case they deviate by a degree exceeding a predetermined value.

The invention relates to a method and an arrangement for monitoring a sensor arrangement comprising a vibration gyroscope which constitutes a resonator and is part of at least one control circuit which excites the vibration gyroscope by feeding an exciter signal at its natural frequency, wherein an output signal can be tapped from the vibration gyroscope and the exciter signal is derived from said output signal by filtering and amplification.

For example EP 0 461 761 B1 has disclosed rotational speed sensors in which a vibration gyroscope is excited in two axes which are oriented radially with respect to a main axis, for which purpose a primary and a secondary control circuit are provided with corresponding transducers on the vibration gyroscope. If such rotational speed sensors are used in vehicles for stabilizing the movement of the vehicle, a fault-free function of the rotational speed sensors is an important precondition for reliable operation of the motor vehicle. For this reason, various devices and methods for monitoring and rotational speed sensors have already been disclosed, for example by WO 2005/01378 A1, redundant analog components and further digital components being used for monitoring.

The object of the present invention is also to improve the monitoring and to detect malfunctions or failures as far as possible in advance.

This object is achieved with the method according to the invention

-   -   in that a first value of the change in temperature compared to         the measurement is calculated from the difference between the         current value of the natural frequency and a value of the         natural frequency which has been previously measured during         adjustment, stored in a memory and measured at a reference         temperature, and from the temperature coefficient of the natural         frequency,     -   in that a second value of the change in temperature compared to         the measurement is calculated from the difference between the         output variables of a temperature sensor at the current         temperature and at the reference temperature stored in the         memory and the temperature coefficient of the temperature         sensor,     -   in that the two calculated values are compared, and     -   in that a fault signal is generated when there is a deviation         which exceeds a predefined amount.

In relevant sensor arrangements, a temperature sensor and a microcontroller are usually present in any case so that no additional hardware expenditure is necessary to carry out the method according to the invention but rather all that is necessary is to implement the measures according to the invention as a program.

If the vibration gyroscope in a sensor arrangement is not in direct thermally conducting contact with the circuits of the sensor arrangement, the circuits generally assume a higher temperature than the vibration gyroscope during operation. In order to permit a correct comparison in this case, there is provision in a development of the method according to the invention for a correction temperature which takes into account thermal conditions which have changed compared to the adjustment of the temperature sensor to be included in the calculation.

This development is preferably embodied in such a way that the correction temperature is calculated from the measured power loss of an integrated circuit which contains the temperature sensor, from the power loss which has been measured during the adjustment and stored in the memory and from the thermal resistance of the integrated circuit with respect to the surroundings.

The invention also comprises an arrangement for monitoring a sensor arrangement comprising means

-   -   in order to calculate a first value of a change in temperature         from the difference between the current value of the natural         frequency and a value of the natural frequency which has been         previously measured during adjustment and stored in a memory,         and from the temperature coefficient of the natural frequency,     -   in order to calculate a second value of a change in temperature         from the difference between the output variables of a         temperature sensor at the current temperature and at the         measurement temperature, and the temperature coefficient of the         temperature sensor,     -   in order to compare the two calculated values, and     -   in order to generate a fault signal when there is a deviation         which exceeds a predefined amount.

The measures specified in the subclaims make possible advantageous developments and improvements of the arrangement according to the invention.

The invention permits numerous embodiments. One of them is illustrated schematically in the drawing and described below. The drawing shows a block diagram of a sensor arrangement comprising a vibration gyroscope with the elements serving to carry out the method according to the invention.

The sensor arrangement and parts thereof are illustrated as block circuit diagrams. However, this does not mean that the sensor arrangement according to the invention is limited to an implementation using individual circuits which correspond to the blocks. The sensor arrangement according to the invention can instead by implemented in a particularly advantageous way using highly integrated circuits. This can be done using microprocessors which, given suitable programming, carry out the processing steps illustrated in the block circuit diagrams.

The sensor arrangement has a vibration gyroscope 1 with two inputs 2, 3 for a primary exciter signal PD and a secondary exciter signal SD. The excitation is effected by means of suitable transducers, for example electromagnetic ones. The vibration gyroscope also has two outputs 4, 5 for a primary output signal PO and a secondary output signal SO. These signals pass on the respective vibration to spatially offset locations on the gyroscope. Such gyroscopes are known, for example, from EP 0 307 321 A1 and are based on the effect of the Coriolis force.

The vibration gyroscope 1 constitutes a high quality filter in which the distance between the input 2 and the output 4 is part of a primary control circuit 6, and the distance between the input 3 and the output 5 is part of a secondary control circuit which is not illustrated since it is not necessary to explain it in order to understand the invention. The primary control circuit 6 serves to excite oscillations at the resonant frequency of the vibration gyroscope of, for example, 14 kHz. The excitation is effected here in an axis of the vibration gyroscope with respect to which the oscillation direction which is used for the secondary control circuit is offset by 90°. In the secondary control circuit which is not illustrated, the signal SO is split into two components, one of which can be tapped, after suitable processing, as a signal which is proportional to the rotational speed.

In both control circuits, a significant part of the signal processing is carried out in digital fashion. The clock signals which are necessary for the signal processing are generated in a quartz-controlled, digital frequency synthesizer 10 whose clock frequency is 14.5 MHz in the example illustrated. For the application of the method according to the invention, the primary control circuit is essentially considered, for which reason an exemplary embodiment of the primary control circuit is illustrated in FIG. 1.

The control circuit has an amplifier 11 for the output signal PO to which an anti-alias filter 12 and an analog/digital converter 13 are connected. Multipliers 14, 15, to which carriers Ti1 and Tq1 are fed, are used to carry out splitting into an in-phase component and a quadrature component. Each of the two components subsequently passes through a (sinx/x) filter 16, 17 and a low pass filter 18, 19. The filtered real part is fed to a PID controller 20 which controls the digital frequency synthesizer, as a result of which a phase control circuit which brings about the correct phase angle of the carriers Ti1 and Tq1 is closed. Furthermore, a carrier Tq2 is generated and it is modulated in a circuit 22 with the output signal of a further PID controller 21 which receives the low pass-filtered imaginary part. The output signal of the circuit 22 is fed to the input 2 of the vibrating gyroscope 1 as exciter signal PD. Instead of the PID controllers it is possible, depending on the conditions, to provide in particular also other controllers, for example PI controllers.

In order to carry out the method according to the invention, a microcontroller 27 is provided which controls the individual steps of the method according to the invention and has access to a nonvolatile memory 28 which is embodied as an EEPROM. In addition, for the method according to the invention a temperature sensor which is present in any case in many sensor circuits is used, said temperature sensor being composed of an actual sensor 29 and an analog/digital converter 30. A bus system 31 connects the specified components to one another and to the digital frequency synthesizer 10 and to the circuit 22.

Within the scope of an adjustment method when the sensor arrangement was manufactured the value FORT of the natural frequency of the vibration gyroscope which was measured then and the temperature at which the measurement was carried out, in the form of the output voltage VRT of the temperature sensor 29, were written into the memory 28.

For the purpose of monitoring, these variables are read out from the memory 28 from time to time during operation and for the purpose of comparison they are compared with the respectively current natural frequency taking into account the current temperature measured with the sensor 29 (output voltage V_(TA)). The comparison is based, for example, on the following equations:

T _(adelta1)=(F _(OTA) −F _(ORT))/T _(CFO)

T _(adelta2)=(V _(TA) −V _(RT))/T _(Cv)

Here, T_(adelta2) is the change in temperature which is detected using the temperature sensor, T_(adelta1) is the change in temperature detected on the basis of the change in the frequency, T_(Cv) is the temperature coefficient of the temperature sensor 29 which is stored in the memory, F_(OTA) is the current frequency, F_(ORT) is the frequency which is stored in the memory and T_(CFO) is the temperature coefficient of the natural frequency of the vibration gyroscope which is likewise stored in the memory.

The current value of the natural frequency can be acquired from the respective setting of the divider of the digital frequency synthesizer 10 and its clock frequency. However, it is also possible to calculate the current value using a frequency measuring device which is composed of a further amplifier 24, a Schmitt trigger 25 and a counter 26.

In an ideal case, T_(adelta1) and T_(adelta2) are identical; if a difference assumes values which exceed a predefined amount, it is possible to infer that one of a plurality of possible faults is present and, for example, a fault can be signaled in the form of the lighting up of a warning lamp or can be stored in the memory in order to be available for later diagnostic purposes.

In order to take into account a power loss, which is different from the adjustment, of the circuit which contains at least the primary control circuit 6, the power drain I of the circuit is measured using a measuring resistor 32 with the value R. The operating voltage U for the circuit is fed to a connection 33 and distributed to the various components via a circuit node 34. The voltage drop U_(i) at the measuring resistor 32 is amplified in an amplifier 35 by a factor v and fed to the analog/digital converter 30 via a multiplexer 36. The microcontroller 27 then calculates the power loss according to the equation P=U*I=U*U_(i)/(R*v). During the adjustment, the power loss P_(RT) and the associated ambient temperature T_(RT) are stored in the memory.

The power loss which is calculated during operation is denoted by P_(A) in the text which follows.

It is therefore possible to calculate a correction temperature, specifically as T_(kor)=T_(RT)+(P_(A)−P_(RT))*R_(TH), where R_(TH) signifies the thermal resistance between the circuit and the surroundings. The abovementioned equation for calculating T_(adelta2) is therefore supplemented as follows:

T _(adelta2kor) =T _(adelta2) −T _(kor)

As already mentioned above, when there is a lack of identity a fault signal can be output, specifically if:

T_(adelta1) ≈T _(adelta2kor). 

1.-8. (canceled)
 9. A method for monitoring a sensor arrangement comprising a vibration gyroscope which constitutes a resonator and forms a part of at least one control circuit which feeds an exciter signal at a natural frequency to excite the vibration gyroscope, wherein an output signal is tapable from the vibration gyroscope and the exciter signal is derived from said output signal by filtering and amplification, the method comprising: calculating a first value of a change in temperature compared to a measurement from a difference between a current value of the natural frequency and the value of the natural frequency previously measured during an adjustment, stored in a memory and measured at a reference temperature, and from a temperature coefficient of the natural frequency; calculating a second value of the change in temperature compared to the measurement from the difference between output variables of a temperature sensor at a current temperature, the reference temperature stored in the memory and the temperature coefficient of the temperature sensor; comparing the first calculated value and the second calculated value; and generating a fault signal when a deviation which exceeds a predefined amount occurs.
 10. The method as claimed in claim 9, further comprising: wherein the step of comparing uses a correction temperature which takes into account thermal conditions which have changed compared to the adjustment of the temperature sensor.
 11. The method as claimed in claim 10, wherein the correction temperature is calculated from the measured power loss of an integrated circuit which contains the temperature sensor, the power loss which has been measured during the adjustment and stored in the memory and from the thermal resistance of the integrated circuit with respect to surroundings of the temperature sensor.
 12. An arrangement for monitoring a sensor arrangement comprising: a vibration gyroscope which constitutes a resonator and forms part of at least one control circuit which feeds an exciter signal at a natural frequency to excite the vibration gyroscope, an output signal being tapable can from the vibration gyroscope and the exciter signal being derived from said output signal by filtering and amplification; and means for calculating a first value of a change in temperature compared to a measurement from a difference between a current value of the natural frequency and the value of the natural frequency previously measured during an adjustment, stored in a memory and measured at a reference temperature, and from a temperature coefficient of the natural frequency, for calculating a second value of the change in temperature compared to the measurement from the difference between output variables of a temperature sensor at a current temperature, the reference temperature stored in the memory and the temperature coefficient of the temperature sensor, for comparing the first calculated value and the second calculated value, and for generating a fault signal when a deviation which exceeds a predefined amount occurs.
 13. The arrangement as claimed in claim 12, wherein the means comprise a microcontroller with a nonvolatile memory.
 14. The arrangement as claimed in claim 12, further comprising: means for using a correction temperature in the comparison which takes into account thermal conditions which have changed compared in comparison to the adjustment of the temperature sensor.
 15. The arrangement as claimed in claim 13, further comprising: means for including a correction temperature in the calculation for taking into account thermal conditions which have changed compared in comparison to the adjustment of the temperature sensor.
 16. The arrangement as claimed in claim 14, further comprising: means for calculating the correction temperature from a measured power loss of an integrated circuit which contains the temperature sensor, from the power loss which has been measured during the adjustment and stored in the memory and from the thermal resistance of the integrated circuit with respect to surroundings of the sensor.
 17. The arrangement as claimed in claim 12, further comprising: means for determining the current value from a respective setting of a divider of a digital frequency synthesizer and a clock frequency of the frequency synthesizer. 